This research is intended to apply the recent pharmacological advances in GABA function physiology in order to more accurately determine GABA's significance in regulation of anterior pituitary secretion. The existing controversy over the physiological significance of GABA to hormone release results from the low potency of GABA in vivo and in vitro. It is now apparent that benzodiazepines and endogenous inhibitor proteins modulate the sensitivity of the GABA receptor. In addition Grandison and Guidotti have observed specific GABA binding receptors in the pituitary. Thus the previous inability of GABA at "physiological doses" to affect hormone release may involve insensitive GABA receptors. We attempt to examine pituitary and hypothalamic GABA function and receptor sensitivity as it relates to the regulation of pituitary hormone secretion. The specificity of GABA action in vitro and in vivo and the interaction between GABA and benzodiazepines, a substitute for a putative endogenous ligand, will be examined. Both biological activity, i.e., action on hormone release, and binding studies will be carried out. Correlation of GABA activity and hormone secretion in vivo will be made using GAD activity and GABA reuptake as measures of GABA function.